EFFICIENCY OF POST-HARTREE-FOCK FORCE-FIELD FOR THE INTERPRETATION OFVIBRATIONAL-SPECTRA OF N,N-DIMETHYLNITRAMINE

Harmonic force fields for the molecule of N,N-dimethylnitramine were c alculated in the RHF/6-31G and MP2/6-31G** approximations. Scaling of the force fields obtained made it possible to reliably interpret the vibrational spectra of light and perdeuterated compounds reported in t he literature. The assignment is confirmed by good reproducibility of experimental isotope shifts upon N-15-amino- and N-15-nitrosubstitutio n. The frequencies of intramolecular vibrations in far IR and Raman sp ectra as well as in neutron inelastic scattering spectra for the light and perdeuterated samples of solid N,N-dimethylnitramine were identif ied using the force field calculated with the inclusion of electron co rrelation (MP2). Although general structures of the force fields calcu lated in the RHF and MP2 approximations are similar, considerable diff erences in the force constants of the NO and NN stretching vibrations and especially in the constants of the NOstr/NOstr and NOstr/NNstr int eractions remain even after scaling the force fields.